diff --git a/llvm/utils/TableGen/InstrInfoEmitter.cpp b/llvm/utils/TableGen/InstrInfoEmitter.cpp
--- a/llvm/utils/TableGen/InstrInfoEmitter.cpp
+++ b/llvm/utils/TableGen/InstrInfoEmitter.cpp
@@ -22,6 +22,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Casting.h"
+#include "llvm/Support/Regex.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
@@ -449,6 +450,31 @@
   OS << "} // end namespace " << Namespace << "\n";
   OS << "} // end namespace llvm\n";
   OS << "#endif // GET_INSTRINFO_OPERAND_TYPE\n\n";
+
+  OS << "#ifdef GET_INSTRINFO_MEM_OPERAND_SIZE\n";
+  OS << "#undef GET_INSTRINFO_MEM_OPERAND_SIZE\n";
+  OS << "namespace llvm {\n";
+  OS << "namespace " << Namespace << " {\n";
+  OS << "LLVM_READONLY\n";
+  OS << "static int getMemOperandSize(int OpType) {\n";
+  OS << "  switch (OpType) {\n";
+  Regex MemSizeRegex("Mem([0-9]+)");
+  for (const Record *Op : Operands) {
+    assert(!Op->isValueUnset("ParserMatchClass"));
+    const Record *OperandClassDef = Op->getValueAsDef("ParserMatchClass");
+    // ParserMatchClass Name field, e.g. Mem64
+    StringRef Name = OperandClassDef->getValueAsString("Name");
+    SmallVector<StringRef> Matches;
+    if (!MemSizeRegex.match(Name, &Matches))
+      continue;
+    std::string Size = MemSizeRegex.sub("\\1", Matches[0]);
+    OS << "  case OpTypes::" << Op->getName() << ": return " << Size << ";\n";
+  }
+  OS << "  default: return 0;\n";
+  OS << "  }\n}\n";
+  OS << "} // end namespace " << Namespace << "\n";
+  OS << "} // end namespace llvm\n";
+  OS << "#endif // GET_INSTRINFO_MEM_OPERAND_SIZE\n\n";
 }
 
 void InstrInfoEmitter::emitLogicalOperandSizeMappings(